The brain is an intricate set of neural circuits that communicate and interact. These circuits are organized at the local spatial scale (microns) of synapses that connect nearby neurons and at the much larger spatial scale (centimeters) of axon bundles that connect widely separated regions of cortex. MRI is a noninvasive measurement method that is the only technique available for measuring axon bundle circuits and tissue properties at the micron scale in the living human brain. The grant proposes new methods to identify circuits in adult brains and then to measure the normal development of tissue properties in key axon bundles. Understanding the circuit characteristics and their healthy development is essential for the goals of monitoring healthy visual development, detecting disease, evaluating the efficacy of therapies, and understanding neural signals needed for proper visual perception. PUBLIC HEALTH RELEVANCE: The visual system comprises an intricate set of neural circuits that are organized at the micron scale of local groups of neurons and as well as the centimeter scale of axon bundles that connect neurons in different parts of cortex. This grant proposes new measurements and algorithms to identify axon bundles and measure tissue properties of these bundles in the visual parts of the brain. Identifying these circuits in adult brains and measuring their normal development in children will allow us to understand the circuit characteristics that are important for healthy visual development and normal visual perception, for detecting and monitoring disease (e.g. optic neuritis or multiple sclerosis) progression, and for evaluating the efficacy of therapies.